Method of making steel low in nitrogen



Nov. 8, 1960 R. F. GRAEF METHOD OF MAKING STEEL LOW IN NITROGEN Filed June 9, 1958 Inventor? 7o n af j? 6 712. e

United States Patent" 2,959,479 METHOD OF MAKING STEEL Low IN NITROGEN Rudolf F. Graef, Oberhausen, Germany, assignor to Hiittenwerk Oberhausen Aktiengesellschaft, Oberhausen, Germany Filed June 9, 1958, Ser. No. 740,938

Claims priority, application Germany June 19, 1957 2 Claims. (Cl. 75-60) The invention relates to a method of making steel low in nitrogen, according to which an oxygen enriched gaseous refining means, preferably technically pure oxygen, is by means of twyers blown into the metal bath contained in a drum rotating about a horizontal or substantially horizontal axis and provided with a fire-v resistant liner. The said twyers extend through openings in the end faces of the drum into the interior of the drum, preferably in an inclined manner, and from above the slag layer through the same below the surface of the bath.

This method is characterized primarily in that it makes possible a highly economical exploitation of the employed oxygen, and permits the refining process to be completed in a short time. As a result thereof, the refining drum can be exploited in a highly economical manner while its liner will have a high life. The said method is furthermore characterized by low losses in iron, i.e. by a low iron content in the slag. I y

The thermic degree of efficiency of this method has furthermore been improved by introducing oxygen into the metal bath through additional twyers which extend above the bath surface into the interior of the refining drum through openings in the end wall thereof. The oxygen conveyed into the bath by said additional twyers is intended to combust the carbon monoxide which rises from the bath during the refining process. In this connection, the oxygen was blown into the bath in form of technically pure oxygen or at least in form of air considerably enriched with oxygen so that nitrogen was kept away from the metal bath to as great an extent as possible in order thereby to prevent the metal bath from becoming enriched with nitrogen.

It is an object of the present invention further to improve the above mentioned drum refining method.

It is also an object of this invention to provide a method of making steel low in nitrogen which, over the heretofore known and above mentioned drum refining method, will make it possible to save considerable quantities of expensive oxygen and to obtain considerable economical advantages.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing illustrating a diagrammatic section through a refining drum as it may be employed in connection with the method of the present invention.

Surprisingly, it has been found that with the above mentioned drum refining method, no material enrichment in nitrogen will occur if for purposes of combusting the carbon monoxide above the bath, atmospheric air, i.e. ordinary non-heated air, is employed. Therefore, when producing steel low in nitrogen in a drum which rotates about a substantially horizontal axis and has an end face with a central opening through which a gaseous refining means is blown in part by twyers immersing below the bath surface and in part by twyers extending into the drum chamber above the surface of 2 the bath, there is, in conformity with the present invention, an oxygen enriched refining means, preferably technically pure oxygen,= blown below the surface of the bath, while ordinary atmospheric air, i.e. non-heated air is blown into said drum chamber above the surface ofthe bath.

In addition to saving considerable quantities of expensive oxygen and yielding considerable economical advantages, the employment of ordinary non-heated airv for combustion of the carbon oxide, in conformity with the present invention yields lower combustion temperatures in the drum chamber. This has a highly favorable effect upon the life of the fire-resistant lining of the refining drum.

An extension of the duration of the refining process over the heretofore employed method need not occur with the method according to the invention because the refining period is primarily determined by the effect of the oxygen blown into the bath below the surface thereof, and because the duration of the refining process may be reduced by-an increase in the quantity of saidoxygen.

The advantage of the method according to the present invention, particularly the obtained saving in expensive high percentage oxygen will become more apparent from the following Example A pig iron which contained the following constituents was treated: V

3.5% C' 0.40 to 0.60% of Si 1.80 to 2% of Mn 0.10 to 0.15% of P 0.050 to 0.070% of'S Refining means with an oxy- 1,000 cubic meters 1,250 cubic meters v Patented Nov. 8, 1960 gen content of blown per hour. per hour. below the bath surface. Refining means blown into 4,100 cubic meters 9,000 cubic meters the drum chamber above per hour. per hour. the bath. Said refining means having an 80% 21% (air).

oxygen content of. Blowing period 55 minutes 70 minutes. Duration of Refining Process. minutes minutes. Oxygen consumption per one 58 cubic meters 60 cubic meters.

ton of pig iron.

0.86 cubic meters.

Oxygen consumption per fiinute per each ton of pig Analysis of the finished steel in percent:

As will be obvious from the above, the consumption in oxygen per one ton of pig iron was in case B only slightly higher than in case A. However, in case B approximately one-third only of the total quantity of oxygen was represented by the expensive concentrated oxygen, whereas approximately two-thirds of the total quantity of oxygen was represented by ordinary air. Nevertheless, the nitrogen content of the finished steel was in case B approximately as low as in case A. I

The quantity of oxygen to be introduced into the metal bath per minute per one ton of pig iron was in case B less than in case A so that the blowing time had naturally to be correspondingly longer and also the duration of the refining process increased correspondingly. However, a reduction in the blowing time and the duration of the refining process could-have -been obtained in case B by increasing the quantityof oxygen to be blown below the bath surface per time unit.

While the method accordin to the present invention may becari'ied out in refining drums of different types, a refining drum suitable for the method of the present invention is shown in the accompanying drawing. In this drawing the refining drum is represented by the rotary drum 1 with a lining 2. Drum 1 res'tsbn rollers 3 by means of running crowns 4gs'ai'clfrollers be'ing'journalled in a base 5. The drum is' provided-witna toothed :rin 6 adapted to mesh with a corresponding gear or driving motor (not shown i'nthe drawing) whichwill' rotate the rotary drum approximately about the longitudinal axis thereof.

The drum has on the left side thereof (with regard to the drawing) a substantially central "opening 7 through which extends a primary nozzle "8 which duringthe' refining operation is immersed to such an extent that the mouth 8110f the nozzle 8 is below the surface of the pig iron bath 9. The nozzle 8 is carriedby a slide 10 movable and adjustable on a track 11. The track 11 is pivotally connected at 12*t'o a carriage 13. It will thus be seen that the nozzle 8 may be' tilted from its shown immersed position into a horizontal position and "by means of carriage 13 can then be withdrawn from the The tiltability of track 11 makes it possible to vary the angle at which the nozzle 8 extends into the metal bath thereby causing the nozzle 8 to extend more or less into said metal bath.

In addition to the nozzle 8 there is also provided a secondary nozzle 14 which blows ordinary, i.e. non-heated air into the drum above the surface of. bath 9. The nozzle 14 may be held in its position by any convenient means.

It is, of course, to be understood that the present invention is, by no means, limited to the particular example set forth in the description and the particular refining drum shown in the drawing but also comprises any modifications within the scope of the appended claims.

What I claim is:

l. .In a method of making steel low in nitrogen in a refining drum rotatable about a substantially horizontal axis, which includes the steps of: placing the pig iron bath to be refined into said drum, and while continuously rotating said drum in complete revolutions about its longitudinal axis; blowing a gaseous oxygen enriched refining means into said bath below the surface thereof and ordinary non-heated air into the drum space above the surface of said bath.

2. In a method of making steel low in nitrogen in a refining drum rotatable about a substantially horizontal axis, which includes the steps of: placing the pig iron bath to 'be refined into said drum, and while continuously rotating said drum in complete revolutions about its longitudinal axis; blowing technically pure oxygen into said bath below the surface thereof and ordinary nonheated air into the drum space above the surface of said bath.

References Cited in the file of this patent UNITED STATES PATENTS Lewis June 9, 1953 Graef Sept. 17, 1957 OTHER REFERENCES 2,641,461 modes? the 

1. IN A METHOD OF MAKING STEEL LOW IN NITROGEN IN A REFINING DRUM ROTATABLE ABOUT A SUBSTANTIALLY HORIZONTAL AXIS, WHICH INCLUDES THE STEPS OF: PLACING THE PIG IRON BATH TO BE REFINED INTO SAID DRUM, AND WHILE CONTINUOUSLY ROTATING SAID DRUM IN COMPLETE REVOLUTIONS ABOUT ITS LONGITUDINAL AXIS, BLOWING A GASEOUS OXYGEN ENRICHED REFINING MEANS INTO SAID BATH BELOW THE SURFACE THEREOF AND ORDINARY NON-HEATED AIR INTO THE DRUM SPACE ABOVE THE SURFACE OF SAID BATH. 